The invention relates to a method for controlling an automatic transmission driven by a prime mover in which a shift from a first to a second transmission ratio occurs in the form of a pull upshift or a push downshift or as pull downshift or push upshift. A first clutch opens and a second one closes and an electronic transmission control device controls, via electromagnetic valves, the pressure curve of the first and second clutch during the shifting operation. The latter consists, in particular, of rapid-filling, filling-equalization, load-transfer, gradient-setting, sliding, gradient-reduction and closing phases.
Such a method is known already from the Applicant""s laid open application DE 44 24 456 A1 which is included by explicit reference in the contents of the preamble of the instant patent application. In the publication is particularly proposed to use this method in a group transmission.
From the prior art (xe2x80x9cThe Engine Interventionxe2x80x9dxe2x80x94a new element of the electronic transmission control by Manfred Schwab and Alfred Mxc3xcller, Bosch, Technical Reports 7, 1983, pp. 166 to 174) is known, in general, to effect an engine intervention during a shifting operation, it being possible by an exactly timed controlled curve of the engine torque during shifting operations of an automatic transmission to optimize the control of the transmission with regard to shifting comfort, service life of the friction elements and the transmissible power of the transmission. By engine intervention is to be understood that all steps which, during a shifting operation in the transmission, allow purposefully to modulate, especially to reduce, the engine torque generated by the combustion process. Due to the legislator""s strict requirement on the reaction time and the time cycle of the control during a total duration of the intervention of only about 500 ms, a precise timed coordination of the shifting operation is required. An engine intervention can be used both in upshifts and downshifts. The primary object of the engine intervention in upshifts is to reduce the energy loss produced in the friction elements during the shifting operation by reducing the engine torque during the synchronization process without interrupting the traction. The tolerance obtained thereby can be used to increase the service life of the friction partners by abbreviating the grinding time.
From DE 42 09 091 A1, a method is further known already for reducing the engine torque during a gear shift in a motor vehicle. The energy torque which results from rotating masses to be retarded or accelerated during a change of speed of the rotation angle of the engine determined by a gear change is calculated here and the engine torque is reduced during coupling of the new transmission gear by the amount of the energy torque.
Methods of the above mentioned kind are subject to constant further development with regard to an optimal use of the engine intervention with the smallest possible load of the shifting elements, an optimal torque curve that takes into account the directives of the engine manufacturer, especially in relation to the limits of the maximum possible engine intervention with regard to mixture and exhaust conditions, the same as to the use of possible advantages in the shifting quality as result of the torque modulation.
The problem to be solved by this invention is to indicate an optimized use of the engine intervention with the purpose of improving the shifting quality by an engine intervention, especially by adapting the output torque during the slipping phase to the output torque at the end of the shift.
According to the invention, this problem is solved in a method of the above mentioned kind by an engine intervention by reduction of the engine torque within the load-transfer, gradient setting, sliding, gradient-reduction and closing phases wherein an engine torque and/or characteristic value that determines the engine torque is transmitted from the transmission control device to an engine control device. Thereby excesses in the breaking in of the output torque in the partial load range can be advantageously presented in shifts of all kinds. The response behavior or the drive dynamics of the transmission is also improved especially during pull downshifts in the partial load range, the shifting element load is reduced and the shifting quality improved in pull upshifts.
In one development of the invention is proposed that the start of the engine intervention for synchronization with the shifting pressure build-up in the GE and GL phases be delayed by a time step when the reaction of the engine to the engine intervention is quicker than the reaction of the transmission to pressure directives. Thereby is advantageously obtained that the output torque be, not unnecessarily reduced.
In reversal of the above mentioned features, it is proposed that the start of the shifting pressure build-up for synchronization with the engine intervention in the GE and GL phases be delayed by a time step when the reaction of the engine to the engine intervention is slower than the reaction of the transmission to pressure directives. Thereby is advantageously obtained that unnecessary frictional loads on the shifting elements be prevented.
In a development of the invention, the dynamic engine torque M_DYN is increased during the gradient-setting phase GE from 0 to 100%, in the sliding phase GL, it remains at 100% and in the gradient-reduction phase GA that follows the dynamic engine torque M_DYN is again reduced from 100% to 0.
When there exist outside the engine other torque-modulating aggregates, such as an electromotor, a dynamo, a fan, an air-conditioning compressor, an additional brake, or others, the engine intervention is distributed among the aggregates so as thereby to enlarge the limited torque range of the internal combustion engine.
The expression engine torque in this case extends to the sum of torques of all aggregates engaged in the transmission input.